On a cold and breezy Manhattan morning New Yorkers awoke yesterday to find their most precious urban landmark transformed into one of the world's biggest ever works of art.

Central Park's drab winter colours of grey and brown are now punctuated with flapping rivers of glowing orange after controversial artists Christo and Jeanne-Claude unveiled their latest project, 'The Gates'.

The artwork consists of 7,500 16-foot high metal gates each bearing a banner of orange fabric that creates rivers of colour on 23 miles of the park's famous paths. The work is the one of the most ambitious ever attempted by the artistic pair, whose previous pieces have included wrapping the Reichstag, a Parisian bridge and part of the Australian coast.

Certainly 'The Gates' has been a long time coming. Christo and Jeanne-Claude, who live in New York, first proposed the work in 1979. Now, a quarter of a century later, their vision has finally become reality. The first five of the orange banners was unfurled by Mayor Michael Bloomberg as a crowd of cheering onlookers counted down to the moment the material was released. Then, over the next two and a half hours, banner after banner dropped from their steel gates until the whole park was running with rivulets of bright colour. In amid the flags thousands of New Yorkers wandered, many of them families, in a party atmosphere. They were joined by many tourists, some of whom had come from across America and the world to see the project. 'It is exceeding my expectations. It is beautiful, it is gorgeous,' said Jamie Ferrer, a young woman from Brooklyn. Others had equally positive reactions, perhaps to be expected from those who had braved the cold to witness the work's opening. 'It's a bit insane, but that's why everybody is here,' said Ali Naqui.

'The Gates' will remain open for 16 days and is expected to attract at least 200,000 tourists. It has already been a huge publicity success for New York. Though the Big Apple rarely needs encouragement to attract media interest, 'The Gates' has been exceptional in the amount of attention it has already grabbed. One city hotel has offered a 'saffron-seasoned' lunch in honour of 'The Gates' orange-yellow colour. Another has put binoculars in all its rooms overlooking the park, while the Metropolitan Museum of Art has opened its summer roof garden to give visitors a better view.

But the interest is far from limited to just New York. At an official press conference on Friday Christo and Jeanne-Claude and Bloomberg faced a phalanx of 45 TV cameras as they discussed the project. Journalists from more than 200 organisations, including from Mexico, Sweden and Bulgaria, strained to hear their every word. Many international tour companies are offering special trips to New York just to see the project.

A grinning Bloomberg, who has aggressively promoted New York arts even as he cut the public art budget, said he believed 'The Gates' would generate at least $80 million for the city. Bloomberg did not hold back in lauding the artistic worth of the piece. He compared 'The Gates' to the Sistine Chapel, Beethoven's Ninth Symphony and Gone With the Wind and noted that 'The Gates' had taken much longer than all of them from its conception to its execution. '[They were] mere blinks of an eye compared to the time that it took to build the masterpiece that we are celebrating today,' he said.

Ironically the artists themselves were much less forthcoming in describing their work. Jeanne-Claude told the assembled reporters that people should not read too much into the work but should just relax and enjoy it. 'It is only a work of art,' the flame-haired artist said. 'It has no purpose. It provides no symbol.'

Christo explained the reason behind the pair's refusal to analyse their own work by saying that it was just intended for people to walk through and enjoy the experience. 'You ask us to talk. This project is not involving talk. It's a real physical space. It is about seeing. You spend time. You experience the project,' he said as he grew visibly irritated at journalists' queries about the inner meaning of 'The Gates'. 'If you are young you should walk all 23 miles. If you are old, two is good,' he snapped.

The scale of the project is huge. 'The Gates' will use 5,290 tons of steel and 60 miles of vinyl tubing. More than 165,000 nuts and bolts will secure the structure along with 116,000 miles of nylon thread. An army of 700 volunteers erected them. The financial cost is also large with the bill coming in at about $20m. Yet the artists provide all the funding and will recoup much of the costs through the sale of studies, scale models and preparatory drawings.

In many ways Christo and Jeanne-Claude typify the stereotype of the avant garde artists. The mysterious husband and wife team, who go only by their first names, met when Jeanne-Claude was a French socialite and Christo was a penniless Bulgarian portrait artist who had escaped his Soviet-run homeland to Paris on a freight train. Since they hit on the idea of wrapping public objects and other large-scale art, the pair have won worldwide acclaim and a loyal following while maintaining an aura of secrecy and eccentricity.

Some of their most famous works include wrapping a chain of islands off the coast of Florida and erecting 3,000 huge umbrellas in valleys in California and Japan. They first began working together in 1960 and their first wrapping project was in 1968 when they used 27,000 square feet of fabric to wrap a building in Switzerland. They say they pay for their own work because it allows them to maintain their artistic independence and integrity. This is necessary when their huge works often involve the co-operation of thousands of people and many different organisations, including city and national governments.

'The Gates' certainly follows in that tradition. It took so long to be built because successive city governments balked at the idea of using Central Park in such a way. It was only when Bloomberg came to office that official obstacles to the work disappeared. But it has not all been plain sailing. The nature of the work means 'The Gates' is open to the public 24 hours a day in a city that was once famed, not for its art, but for its high crime rate. Though Central Park is much safer these days, 'The Gates' still poses a huge security problem and a target for vandals.

As a result, New York's police department has dispatched helicopters to monitor the work and built a round-the-clock command centre in the park's boathouse. They have added several hundred officers to the park's already 125-strong force. Typically, Christo and Jeanne-Claude are footing the entire extra security bill.

$21 million, 7,500 gates, one dream

· It consists of 7,500 gates, standing 16ft tall and about 12ft apart, which line 23 of Central Park's 56 miles.

· Over half of the park's pathways will not feature The Gates, due to the duo's commitment not to disturb any vegetation.

· City and Parks officials have predicted that The Gates will draw half a million tourists to New York, and crowds of as many as 200,000 people.

· The steel bases of The Gates have been constructed to be able to withstand the most powerful gust of wind of the last half-century.

· More than 10 million pounds of raw steel went into making the attraction. After the installation, they'll be sent to an industrial-recycling company.

· German manufacturer J Schilgen Company wove 119,556 miles of thread to produce 1,006,620 square feet of rip-stop nylon for the installation.

· Arguably, the best place to view The Gates is from Summit Rock, which is the highest elevation in the park.

· 660 New Yorkers were asked about their opinions on the project. The Gates was found to be more popular among the poor than among the rich.

· The artists are paying for the project, which may have cost up to $21 million, themselves. They first dreamt it up years ago, in 1979.

· 'The Gates' is the pair's first project since 'Wrapped Reichstag' in 1995.